Method for detecting compressor surge in a fuel cell system using a mass flow meter

ABSTRACT

A method for detecting compressor surge in a fuel cell system. The system includes a turbomachine compressor that delivers charge air to the cathode side of a fuel cell module. A bi-directional mass flow meter measures the airflow through the compressor, and provides an indication of a reverse airflow through the compressor for surge protection. A controller receives a signal from the mass flow meter indicative of the reverse flow. The controller controls a motor driving the compressor and a back pressure valve at the cathode exhaust of the fuel cell module to control the pressure in the fuel cell module to remove the surge condition.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional application of U.S. patent applicationSer. No. 10/696,279 filed Oct. 29, 2003 now U.S. Pat. No. 7,396,604,titled “Centrifugal Compressor Surge Detection Using a Bi-DirectionalMFM in a Fuel Cell System.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a method for detecting compressorsurge in a fuel cell system and, more particularly, to a method fordetecting compressor surge in a fuel cell system using a bi-directionalmass flow meter (MFM) that measures airflow to and from a turbomachinetype compressor.

2. Discussion of the Related Art

Hydrogen is a very attractive fuel because it is clean and can be usedto efficiently produce electricity in a fuel cell. The automotiveindustry expends significant resources in the development of hydrogenfuel cells as a source of power for vehicles. Such vehicles would bemore efficient and generate fewer emissions than today's vehiclesemploying internal combustion engines.

A hydrogen fuel cell is an electro-chemical device that includes ananode and a cathode with an electrolyte therebetween. The anode receiveshydrogen gas and the cathode receives oxygen or air. The hydrogen gas isdisassociated in the anode to generate free hydrogen protons andelectrons. The hydrogen protons pass through the electrolyte to thecathode. The hydrogen protons react with the oxygen and the electrons inthe cathode to generate water. The electrons from the anode cannot passthrough the electrolyte, and thus are directed through a load to performwork before being sent to the cathode. The work acts to operate thevehicle.

Proton exchange membrane fuel cells (PEMFC) are a popular fuel cell forvehicles. The PEMFC generally includes a solid polymer electrolyteproton conducting membrane, such as a perfluorosulfonic acid membrane.The anode and cathode typically include finely divided catalyticparticles, usually platinum (Pt), supported on carbon particles andmixed with an ionomer. The combination of the anode, cathode andmembrane define a membrane electrode assembly (MEA). MEAs are relativelyexpensive to manufacture and require certain conditions for effectiveoperation. These conditions include proper water management andhumidification, and control of catalyst poisoning constituents, such ascarbon monoxide (CO).

Many fuel cells are typically combined in a fuel cell stack to generatethe desired power. The fuel cell stack receives a cathode charge gasthat includes oxygen, and is typically a flow of forced air from acompressor. Not all of the oxygen in the air is consumed by the stackand some of the air is output as a cathode exhaust gas that may includewater as a stack by-product.

FIG. 1 is a plan view of a fuel cell system 10 including an air deliverysub-system 12 and a fuel cell module (FCM) 14 having a fuel cell stackof the type discussed above. The sub-system 12 includes a turbomachinecompressor 16 that provides charge air to the cathode side of the FCM14. The compressor 16 can be any suitable turbomachine type compressor,such as a centrifugal, radial, axial, mixed flow, etc., compressor. Thistype of compressor is desirable in the system 10 because it is low costand low weight, and operates with low noise as compared to the positivedisplacement compressors, such as twin-screw compressors, that arecurrently employed in fuel cell systems. The hydrogen fuel input to theFCM 14 is not shown in this diagram. Cathode exhaust, including unusedair and water, is emitted from the FCM 14 through a cathode exhaust line26. A back pressure valve 24 in the cathode exhaust line 26 is openedand closed to control the pressure within the FCM 14, and thus, controlstack pressure, membrane humidity, etc.

A motor 18 drives the compressor 16 at the appropriate speed to providethe desired amount of charge air to the FCM 14 for the desired outputpower. Air from the environment is filtered by a filter/attenuator 20that also reduces compressor whine. The filtered air is sent through amass flow meter (MFM) 22 that measures the airflow through thecompressor 16. A signal indicative of the airflow through the compressor16 from the MFM 22 is sent to a controller 28. The controller 28controls the speed of the motor 18 to control the airflow through thecompressor 16 to provide the proper air stoichiometry or lambda. Thecontroller 28 also controls the orientation of the back pressure valve24 to control the pressure within the FCM 14, and thus, membranehumidity. Many factors determine the speed of the compressor 16,including desired output power, ambient temperature, altitude, etc.

It is necessary that the compressor 16 operate on its map of pressureratio (outlet pressure/inlet pressure) versus air flow. This map ofpressure ratio is bound by a surge line at which the compressor 16suffers from an audible flow reversion caused by excessive backpressureas a result of the stack pressure within the FCM 14. This backpressureis generally caused by the back pressure valve 24. In other words, thepressure within the FCM 14 sometimes causes a reverse flow of airthrough the compressor 16 that is determined by the drive power from themotor 18, the altitude and the temperature. The map of the pressureratio is also bound by a choke line where the maximum airflow is reachedwith minimal pressure for a given compressor speed.

The compressor 16 cannot operate at pressure ratios that put thecompressor 16 into a surge condition because of severe oscillation ofthe airflow through the compressor 16 that could damage the compressor16. Therefore, the system 10 requires a surge protector that identifiesa reverse airflow through the compressor 16 to prevent compressor surge.A reverse airflow through the known positive displacement compressorsdid not present a problem or cause compressor damage, and thus, surgedetection is typically not required on known fuel cell systems.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a method fordetecting compressor surge in a fuel cell system is disclosed. Thesystem includes a centrifugal compressor that delivers charge air to thecathode side of a fuel cell module. A bi-directional mass flow metermeasures the airflow to the compressor, and provides an indication of areverse airflow through the compressor for surge protection purposes. Acontroller receives a signal from the mass flow meter indicative of thedirection of the charge airflow, and thus, an indication of whether thecompressor is under surge. The controller controls a motor that drivesthe compressor and controls a back pressure valve at the cathode exhaustof the fuel cell module to control the pressure in the fuel cell moduleto remove the surge condition if detected.

Additional advantages and features of the present invention will becomeapparent from the following description and appended claims, taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a known fuel cell system including an airdelivery sub-system; and

FIG. 2 is a plan view of a fuel cell system including an air deliverysub-system having a bi-directional mass flow meter for measuring reverseairflow through a centrifugal compressor to prevent compressor surges,according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description of the embodiments of the invention directedto a method for detecting compressor surge in a fuel cell system using abi-directional mass flow meter is merely exemplary in nature, and is inno way intended to limit the invention or its applications or uses.

FIG. 2 is a plan view of a fuel cell system 30 including an air deliverysub-system 32, according to an embodiment of the present invention. Thesystem 30 is similar to the system 10 discussed above, where likereference numerals identify like elements. In this design, the airdelivery sub-system 32 includes a bi-directional MFM 34 that measuresairflow through the centrifugal compressor 16 in both directions.Because the MFM 34 is capable of detecting airflow in both directions,it acts as a surge protection device to detect backpressure to thecompressor 16 from the FCM 14. In one embodiment, the MFM 34 is a knownbi-directional MFM sometimes used in small four cylinder gas engines tomeasure the reverse pulse generated by the engine to accurately measurethe incoming airflow by subtracting out the reverse pulse or flowreversal. However, other types of bi-directional flow meters that aresuitable for the purposes discussed herein can be used for the MFM 34.

The MFM 34 provides a voltage signal indicative of the direction andspeed of the airflow through the MFM 34 to a controller 36. The voltagelevel of the signal from the MFM 34 is an indication of the direction ofthe airflow through the MFM 34, and thus, an indication of whether thecompressor 16 is under surge. Therefore, the controller 36 can provide asignal to the motor 18 to speed up the compressor 16 to provideadditional positive pressure to the FCM 14 to eliminate the surgecondition if detected. Additionally, the controller 36 can provide asignal to open the back pressure valve 24 and reduce the pressure withinthe FCM 14 to also remove the surge condition. Also, the controller 36can open a by-pass valve 38 in the exhaust line 26 so that the pressureat the output of the compressor 16 is reduced to eliminate the surgecondition.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

1. A method for detecting and eliminating a surge condition of acompressor in a fuel cell module, said method comprising: detecting areverse airflow through the compressor using a bi-directional mass flowmeter; and preventing compressor surge in response to the detectedreverse airflow.
 2. The method according to claim 1 wherein preventingcompressor surge includes increasing the speed of the compressor inresponse to the detected reverse airflow.
 3. The method according toclaim 1 wherein preventing compressor surge includes opening a backpressure valve in a cathode exhaust line of the fuel cell module inresponse to the detected reverse airflow.
 4. The method according toclaim 1 wherein preventing compressor surge includes opening a by-passvalve in a cathode exhaust line of the fuel cell module in response tothe detected reverse airflow.
 5. The method according to claim 1 whereinthe bi-directional mass flow meter detects the flow of air in both aforward and a reverse direction.
 6. The method according to claim 1wherein the mass flow meter is positioned upstream of the compressor andreceives the airflow below the compressor.
 7. The method according toclaim 1 wherein the compressor is a turbomachine compressor.
 8. Themethod according to claim 1 wherein the compressor is selected from theconsisting of centrifugal, radial, axial and mixed flow compressors. 9.A method for detecting and eliminating a surge condition of a compressorin a fuel cell system, said method comprising: providing an airflow fromthe compressor to a cathode input of the fuel cell system; measuring theairflow sent to the compressor using a bi-directional mass flow meter inboth a forward direction and a reverse direction; and preventingcompressor surge in response to an airflow in the reverse directionthrough the compressor from the cathode input.
 10. The method accordingto claim 9 wherein preventing compressor surge includes increasing thespeed of the compressor in response to the detected reverse airflow. 11.The method according to claim 9 wherein preventing compressor surgeincludes opening a back pressure valve in a cathode exhaust line of thefuel cell module in response to the detected reverse airflow.
 12. Themethod according to claim 9 wherein preventing compressor surge includesopening a by-pass valve in a cathode exhaust line of the fuel cellmodule in response to the detected reverse airflow.
 13. The methodaccording to claim 9 wherein the mass flow meter is positioned upstreamof the compressor and receives the airflow below the compressor.
 14. Themethod according to claim 9 wherein the compressor is a turbomachinecompressor.
 15. The method according to claim 9 wherein the compressoris selected from the consisting of centrifugal, radial, axial and mixedflow compressors.